The primary goal of this Program Project is to better understand age- related changes in sleep timing and structure. To this end, two clinical projects (Project 1 and 4) are proposed, each with sleep and/or waking cortical activity as a primary outcome measure. Given the importance of these outcome measures for both Projects, a separate Core was developed to ensure the accurate and efficient collection, interpretation, and analysis of physiological measures of sleep and wakefulness. Core C will allow for the utilization of shared facilities, equipment, and personnel for the collection and analysis for physiological data for evaluation sleep, as assessed by polysomnogram (PSG) and walking cortical activity, as assessed by electroencephalogram (EEG). Data collection will be carried out by highly trained research technicians in Core C and in the GCRC, all of whom have significant experience with investigations such as these. Sleep scoring and quantification of EEG activity will be carried out by highly trained Registered Polysomnographic Technicians under the close supervision of the Core leader. In addition to the responsibilities for research data collection and analysis, Core C will be responsible for the scoring, interpretation, and evaluation of diagnostic PSG screening to be done on all potential research subjects prior to empanelment in the studies.